I'm a returning Magic player (last played in '03 or so) and first time MTGO player (so far, my experience in MTGO is 4 matches of Just-For-Fun Momir).

I heard of this format as a deck format option when going to Tappedout to work out a deck idea, and it came up as a format option. It brought me here, I read the rules, and it sounds like a fun format. However, I don't see it listed under the Constructed Open format options.

This format is not officially supported in any capacity by wotc or mtgo. It took years and years for EDH (commander) to make it officially, and we are unfortunately nowhere near as popular. Your best bet is to get some friends together to make some paper decks and have fun. One of the goals of the format was to make it accessible by players who were not looking to spend hundreds of dollars on a deck, but still have some of the power that rares and mythics bring to the formats. With that in mind, even if you were to have to construct a half dozen Noble decks to show off how fun it is to friends it would not be too expensive as far as mtg decks go. I personally only have 6 or 7 paper decks, but have constructed dozens on tappedout, as you can probably see on our decklist page.